When she gets a once-in-a-lifetime job opportunity in LA, he jeopardises his witness protection identity in order to drive her to the interview. If you can believe it, things don't go to plan and the pair are pursued by a merry band of nutters including a hapless US marshal, a creepy ex-boyfriend and Charlie's shady former crew led by a dreadlocked Bradley Cooper.

Real-life couple Bell and Shepard strike up an endearingly natural chemistry on-screen, but once the caper gets going Bell's relegated to a passive and largely humourless role. She's by far the most likeable performer in the bunch, witty, warm and spontaneous, but she spends most of the road trip portion being dragged around like a rag doll while the male characters face off.

Shepard doesn't have the same natural charisma, and as Charlie starts to slip back into his old self en route to LA - making a range of off-colour comments that range from homophobic to racist to rapey - it becomes harder and harder to enjoy spending time with him.Having Bell's character indignantly point out his dull-witted stereotyping doesn't make it any less irritating, especially since we're meant to root for her to end up with the moron.

In fact, Hit and Run's main problem is that it partakes enthusiastically in all the things it's theoretically mocking. We're meant to roll our eyes indulgently at Charlie's ignorance, but still see him as the lovable, roguish hero who deserves to get the girl. Similarly the male characters' fetishistic love for their cars gets a ribbing, but then the film indulges in a series of loud, lengthy freeway chase sequences which serve no purpose whatsoever besides indulging that very macho obsession.

The film's not without genuine laughs, but it's so meandering and haphazard that they never quite land with the impact they should. With the exception of Cooper (who lands a decent one-liner or two) and Kristen Chenoweth in a brief role (ditto), the supporting characters fall flat. Tom Arnold's loud, dumb marshal provides below-average slapstick, while a subplot involving a cop obsessed with an app called 'Pouncer' (get it?) seems to stretch out endlessly without really going anywhere.

Not unlike Shepard's Charlie, Hit and Run initially offers some offbeat charm, but reveals itself as a smug, aimless mess once it gets out on the open road.